This invention pertains to projection screens, and, in particular, to a masking apparatus for a projection screen which masks border regions of the projection screen to adjust the dimensions of the viewing surface of the screen.
Projection screens in various forms are being utilized in a variety of venues, including conference rooms and home entertainment systems. On occasion, a projection screen which is appropriately dimensioned for one particular use may be used in a manner which results in portions of the projection screen being superfluous. For example, a single video projection screen provided with a rectangular viewing surface may be called upon for use with different video formats such as normal video projection and high definition television (HDTV). Normal video production has a 3:4 format, meaning the total height of the image projected on the viewing surface is three-quarters of the total width. On the other hand, HDTV utilizes a 9:16 format. Consequently, for video projection screens appropriately sized for a specific one of these formats, these screens will include exposed but unused portions of the viewing surface when utilized with the other format. Thus, to properly frame the projected image, it is desirable to provide a masking apparatus which temporarily masks or covers those portions of the viewing surface of a projection screen upon which no image is to be projected.
A variety of known masking systems have been utilized to mask various regions of projection screens. While some systems have been adequate from the standpoint of successfully covering a particular region of a projection screen, these systems suffer from an assortment of shortcomings. For instance, while a variety of systems have advantageously utilized a single motor to mask multiple borders of a projection screen, typically complex linkages which complicate construction have previously been employed. Another shortcoming relates to the relatively large amount of space occupied by the masking system. In a variety of systems in which an upper region of a projection screen was masked, the masking curtains were suspended from linkages above the curtains. Furthermore, the masking curtains were raised from a masking orientation in accordion fashion or entirely as a panel. As a result, the vertical profile of the system was increased. A known masking system has also attempted to mask the side regions of a viewing surface with curtains which, when not in a masking orientation, were wound around a vertically oriented roller. However, as masking curtains or fabrics may not roll up well around vertically oriented rollers, the performance of these types of masking system may suffer. Thus, it is desirable to provide a masking system for a projection screen which is free from these shortcomings.